Because: Her Little Mermaid demeanor belies a will of steel—exercised on behalf of the world's endangered whales and dolphins.

Photographed: On April 27, off Dana Point, California.

The Story: Growing up in Palisades, New York, the closest thing Hayden Panettiere had to an ocean was the Hudson River. But now, she lends her name and donates her time on behalf of whales and dolphins. An animal lover since childhood, she got involved in 2005, at the age of 15, when she visited a threatened breeding ground for gray whales in Mexico. In Taiji, Japan, she joined documentarian Louie Psihoyos and a team of ninja surfers who paddled out under cover of night to film the wholesale slaughter of dolphins. In the resulting Oscar-winning film The Cove, Panettiere appears in her wet suit, weeping over the plight of the animals. Today, at the ripe old age of 22, she is the spokesperson for the Whaleman Foundation, which fights to protect whales and dolphins from climate change, pollution, entanglements in fishing nets, and the expansion of whaling. "I'm an activist who's aware of what's realistic to achieve and what's not," says Panettiere, who recently starred in the movie Scream 4. Her environmental work continues: Besides social networking and lobbying Congress, Panettiere recently swam with dolphins in Hawaii for an upcoming documentary. "I wouldn't waste my time going straight for the jugular—I'm not going to preach to people to not eat meat," she says. "[The Whaleman Foundation's goals] are achievable, and they make sense." To help, donate at whaleman.org.

The Big Trip: "We knew we were up against a huge obstacle in Taiji. In the course of the slaughter, I saw a species in need. The trip inspired me to continue the fight."

The Tip: "I love singing karaoke in Japan. It is a common ground for me, an enjoyable and bonding experience."